Wireless charging system and method

ABSTRACT

A wireless charging system can optimize charging efficiency regardless of a location of a mobile terminal. The wireless charging system wirelessly charges a mobile terminal using electromagnetic induction between a first coil included in a charging pad and a second coil included in the mobile terminal. The charging pad can detect a location of the mobile terminal on the charging pad. The charging pad can move the first coil to correspond to the detected location of the mobile terminal; and supply power to the first coil and charging a battery.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/655,021, filed Dec. 22, 2009, entitled “WIRELESS CHARGING SYSTEM ANDMETHOD” , which claims priority to an application entitled “WIRELESSCHARGING SYSTEM AND METHOD” filed in the Korean Intellectual PropertyOffice on Dec. 24, 2008 and assigned Serial No. 10-2008-0133078, thecontents of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a wireless charging system and method,and more particularly, to a wireless charging system and method for amobile terminal that can optimize charging efficiency regardless of alocation of a mobile terminal.

BACKGROUND OF THE INVENTION

Nowadays, mobile terminals provide various functions such as a wirelessInternet function, electronic note function, multimedia photographingand reproducing function, and game player function, digital broadcastingfunction in addition to a basic communication function. Such a mobileterminal generally uses a battery for portability.

The battery of the mobile terminal requires electric charging. A methodof charging the battery can be classified into wired charging andwireless charging. The wired charging method is generally used, however,a wireless charging system using an electromagnetic induction phenomenonhas been developed. Such a wireless charging system applies power to acharging pad including a coil (hereinafter, a first coil) at the insidethereof, and charges a battery using an induced current generating in acoil (hereinafter, a second coil) included in a mobile terminal, or abattery using a magnetic field generating in the first coil. That is,the wireless charging system can easily charge a battery by positioningthe mobile terminal on a charging pad generating a magnetic field.However, such a wireless charging system has different chargingefficiency according to a location relationship of the first coil andthe second coil. In other words, when the first coil and the second coilare positioned to correspond, the wireless charging system has the bestcharging efficiency. That is, the wireless charging system should bepositioned at the mobile terminal at a specified location in order tosustain optimum charging efficiency. In order to solve the problem,conventionally, a method of mounting a plurality of first coils, or amethod of largely forming the first coil in order to cover an entirecharging pad area was used. However, such a conventional method has aproblem that wireless communication performance is deteriorated due toan influence of a magnetic field generating by the first coil andbecause the magnetic field is induced in a high and wide area,performance and a lifetime of parts of a mobile terminal may beinfluenced. Therefore, a wireless charging system and method in which amagnetic field generated by the first coil does not deteriorate wirelesscommunication performance of the mobile terminal and that securestability of the mobile terminal and that optimize charging efficiencyare requested.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object to provide a wireless charging system and method thatsecure stability of a mobile terminal by minimizing an influence onperformance and a lifetime of parts of the mobile terminal, and thathave no influence on wireless communication performance, and thatsustain optimum charging efficiency regardless of a location of themobile terminal.

In accordance with an aspect of the present invention, a method forwirelessly charging a mobile terminal using electromagnetic inductionbetween a first coil included in a charging pad and a second coilincluded in the mobile terminal includes: detecting a location of themobile terminal on the charging pad; moving the first coil to correspondto the detected location of the mobile terminal; and supplying power tothe first coil and charging a battery.

In accordance with another aspect of the present invention, a wirelesscharging system using an electromagnetic induction phenomenon includes:a charging pad including a first coil that generates a magnetic fieldwhen power is supplied; and a mobile terminal including a second coilthat charges a battery using an induction current induced to the secondcoil when the magnetic field is generated in the first coil, wherein thecharging pad determines a contact location of the mobile terminal andmoves the first coil to correspond to the location of the mobileterminal.

In accordance with another aspect of the present invention, an apparatusfor charging a battery of a mobile terminal electromagnetic inductionincludes: a charging pad comprising a first coil configured to generatea magnetic field when power is supplied, wherein the first coil isadapted to electromagnetically couple to a second coil included in amobile terminal such that an induction current is induced to the secondcoil in response to a magnetic field generated in the first coil, andwherein the charging pad is configured to determine a location of themobile terminal and move the first coil to correspond to the location ofthe mobile terminal.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates a wireless charging system according to an exemplaryembodiment of the present invention;

FIGS. 2A and 2B illustrate cross-sectional views of charging pads in thewireless charging system of FIG. 1;

FIG. 3 illustrates a configuration of the charging pad of FIGS. 2A and2B;

FIG. 4 illustrates a configuration of a mobile terminal in the wirelesscharging system of FIG. 1;

FIG. 5 illustrates a charging process in the charging pad of FIG. 3; and

FIG. 6 illustrates a process of charging the mobile terminal of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 6, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged portable terminal.

While the present invention may be embodied in many different forms,specific embodiments of the present invention are shown in drawings andare described herein in detail, with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to thespecific embodiments illustrated.

In the following description, a “charging pad” is a charging device forwireless charging of a mobile terminal. “Charging efficiency” indicatesa degree in which electric power supplied for charging in the chargingpad is transmitted to the mobile terminal by electromagnetic inductionphenomenon.

FIG. 1 illustrates a wireless charging system according to an exemplaryembodiment of the present invention. FIGS. 2A and 2B illustratecross-sectional views of charging pads in the wireless charging systemof FIG. 1.

Referring to FIG. 1, 2A, and 2B, the wireless charging system accordingto the present exemplary embodiment includes a mobile terminal 200 and acharging pad 100.

The charging pad 100 is a device for wireless charging a battery of themobile terminal 200. The charging pad 100 includes a first coil thatreceives power to generate a magnetic field and a detection unit 160that detects a contact and a contact location of the mobile terminal 200on the charging pad 100. When a contact of the mobile terminal 200 isdetected through the detection unit 160, the charging pad 100 determinesa location of the mobile terminal 200 and moves the first coil tocorrespond to the mobile terminal 200. Thereby, the charging pad 100 cansubstantially always sustain optimum charging efficiency regardless of alocation of the mobile terminal 200. Further, when the mobile terminal200 contacts on the charging pad 100, the charging pad 100 determineswhether the mobile terminal 200 is a certified device and charges only acertified mobile terminal.

The charging pad 100 includes a projection 170 at an edge thereof, asshown in FIG. 2A, or includes an inclined edge, as shown in FIG. 2B.This is to prevent charging efficiency from becoming deteriorated bypositioning a mobile terminal at a location at which the first coilcannot move. A detailed configuration of the charging pad 100 isdescribed later with reference to FIG. 3.

The mobile terminal 200 can perform wireless charging and includes asecond coil that can generate an induced current according to a changeof a magnetic field generating in the charging pad 100. The mobileterminal 200 charges a battery using the induced current. Here, awireless charge principle uses a Maxwell's equation and becomes apparentto those skilled in the art. Therefore a detailed description thereof isomitted. Further, the mobile terminal 200 determines charging efficiencyby determining the induced current or voltage value. In this case, ifthe charging efficiency is less than a preset reference value, themobile terminal 200 transmits a control signal for moving a location ofthe first coil to the charging pad 100. Further, the mobile terminal 200determines a charging state of a battery and transmits, if electriccharging is complete, a charging completion signal to the charging pad100. For this, the mobile terminal 200 performs magnetic fieldcommunication using the charging pad 100 and a change of a magneticfield. A detailed description of a configuration of the mobile terminal200 is described with reference to FIG. 4.

By determining a location of the mobile terminal 200 and moving thefirst coil and the second coil to correspond thereto, the wirelesscharging system optimizes charging efficiency regardless of a locationof the mobile terminal 200. Therefore, a charging time period can beminimized and a charging pad 100 for general mobile terminal, not aspecific mobile terminal can be designed.

FIG. 3 illustrates a configuration of the charging pad 100 of FIGS. 2Aand 2B.

Referring to FIG. 3, the charging pad 100 according to the presentexemplary embodiment includes a first controller 110, first storage unit120, first coil 140, driver 150, and detection unit 160.

The detection unit 160 is a sensor that detects a contact and a locationof the mobile terminal 200. The detection unit 160 can use a pressuredetection sensor and is positioned at an upper surface of the chargingpad 100 with which the mobile terminal 200 contacts. That is, when themobile terminal 200 contacts the charging pad 100, the detection unit160 detects a location of the mobile terminal 200 and outputs thelocation of the mobile terminal 200 to the first controller 110. In thiscase, the first controller 110 controls the driver 150 to move the firstcoil 140 to a location where the mobile terminal 200 is positioned.

The driver 150 moves the first coil 140 by the control of the firstcontroller 110. That is, the driver 150 moves the first coil 140 to alocation corresponding to the mobile terminal 200 by the control of thefirst controller 110. Thereby, the wireless charging system according tothe present exemplary embodiment can substantially always sustainoptimum charging efficiency regardless of a location of the mobileterminal 200.

The driver 150 can be designed with various methods. For example, thedriver 150 includes a first driver for moving in a horizontal directionand a second driver for moving in a vertical direction.

The first coil 140 can be an electromagnet for generating a magneticfield when power is supplied. The first coil 140 may be, for example, asolenoid. A magnetic field generated in the first coil 140 induces amagnetic field to the second coil included in the mobile terminal 100.The magnetic field induced to a second coil can generate the inducedcurrent. Particularly, in the present exemplary embodiment, when thecharging is requested, the first coil 140 is moved to a locationcorresponding to the mobile terminal 200 on the charging pad 100 by thedriver 150. It is preferable that the first coil 140 is dimensioned tobe small in size to prevent wireless communication performance of themobile terminal 200 from being deteriorated by an influence of amagnetic field.

The first storage unit 120 stores a program necessary for operating afunction of the charging pad 100. Particularly, in the present exemplaryembodiment, the first storage unit 120 stores a communication programfor communicating with the mobile terminal 200. The communicationprogram may be a communication program using a change of a magneticfield. Further, the first storage unit 120 stores first certificationinformation for determining whether the mobile terminal 200 is achargeable device. The reason of performing a certification process isto prevent damage, for example overheating or magnetic damage of anuncertified electronic device due to a magnetic field generated in thefirst coil 140.

The first controller 110 controls general operations of the charging pad100 and a signal flow between units, and performs a data processingfunction. Particularly, in the present exemplary embodiment, when acontact of the mobile terminal 200 is detected through the detectionunit 160, the first controller 120 determines whether the mobileterminal 200 is a chargeable certified device. This is to prevent, whenan object such as a purse is positioned on the charging pad 100, amagnetic strip of a credit card and a traffic card from being damageddue to a magnetic field.

When the mobile terminal 200 is a certified device, the first controller110 determines a location of the mobile terminal 200 and moves the firstcoil 140 to a location corresponding to the mobile terminal 200.Thereafter, when a control signal for requesting location movement ofthe first coil 140 is received from the mobile terminal 200, the firstcontroller 110 moves a location of the first coil 140. The reason ofmoving the location of the first coil 140 according to the controlsignal is that charging efficiency may not optimize with a singleposition because the second coil is positioned at different locations ineach mobile terminal 200.

When a charge completion signal is receive from the mobile terminal 200,the first controller 110 terminates electric charging by interruptingpower supply to the first coil 140. In this case, the first controller110 moves the first coil 140 to a location that does not correspond tothe mobile terminal 200. This is to prevent phenomenon in which electriccharging is not terminated due to power being leaked to the first coil140.

The first controller 110 performs wireless communication by generating amagnetic field with the mobile terminal 200 through the second coil.However, the charging pad 100 is not limited to a charging pad 100 forperforming wireless communication with the mobile terminal 200 using amagnetic field. The charging pad 100 may include, for example, aseparate short range wireless communication module.

FIG. 4 illustrates a configuration of the mobile terminal 200 in thewireless charging system of FIG. 1.

Referring to FIG. 4, the mobile terminal 200 according to the presentexemplary embodiment includes a second controller 210, second storageunit 220, display unit 230, battery 240, charging unit 250, and secondcoil 260.

When a magnetic field generates in the first coil 140 of the chargingpad 100, the second coil 260 induces a magnetic field according toelectromagnetic induction phenomenon. In this case, the second coil 260generates an induced current. Such an electromagnetic inductionprinciple is well known and therefore a detailed description thereof isomitted.

It is preferable that the second coil 260 is shielded from anotherelectronic circuit. This is to prevent a circuit from being damaged by amagnetic field generated in the second coil 260.

In the foregoing description, the second coil 260 includes a separatestructure, however the present invention is not limited thereto. Thatis, the second coil 260 may be included in the battery 240.

The charging unit 250 charges the battery 240 using the induced current.For this, the charging unit 250 includes a charging circuit and anovercurrent or overvoltage protection circuit.

In order to drive the mobile terminal 200, the battery 240 suppliespower to each of the units. The battery 240 can be detached and may be arechargeable battery. As described above, the battery 240 may includethe second coil 260.

The display unit 230 displays user data input by a user, functionsetting information, or various information provided to the user as wellas various menu screens of the mobile terminal 200. Further, when thedisplay unit 230 is formed as a touch screen, the display unit 230 canbe operated as an input means. The display unit 230 can be formed with aliquid crystal display (LCD) or organic light emitting diodes (OLED).Particularly, in the present exemplary embodiment, the display unit 230can display a state of the battery 240 under the control of the secondcontroller 210. That is, the display unit 230 can display a residualamount of a battery, an icon notifying that a battery is being charged,and a charging completion message by the control of the secondcontroller 210.

The second storage unit 220 can store user data as well as a programnecessary for a function operation of the mobile terminal 200 accordingto the present exemplary embodiment. The second storage unit 220includes a program area and a data area.

The program area stores a program for controlling general operations ofthe mobile terminal 200 and an operating system for booting the mobileterminal 200. Particularly, in the present exemplary embodiment, theprogram area includes a wireless communication program for performingcommunication using a change of a magnetic field.

The data area stores data generated according to a use of the mobileterminal 200 and can store information corresponding to a phonebook,audio data, content, or user data. Particularly, in the presentexemplary embodiment, the data area stores a reference value fordetermining charging efficiency. If charging efficiency is less than thereference value, the second controller 210 determines that the firstcoil 140 and the second coil 260 are not positioned at correspondingpositions and transmits a control signal for requesting locationmovement of the first coil 140 to the charging pad 100.

The second controller 210 controls general operations of the mobileterminal 200 and a signal flow between units of the mobile terminal 200,and performs a data processing function. Particularly, in the presentexemplary embodiment, if the charging efficiency is less than thereference value, the second controller 210 transmits a control signalfor requesting to move a location of the first coil 140 to the chargingpad 100. Thereby, the wireless charging system according to the presentexemplary embodiment can sustain optimum charging efficiency. Further,the second controller 210 determines a charging state of the battery 240and when electric charging is complete, and the second controller 210terminates electric charging by transmitting a charging complete stateto the charging pad 100. For this, the second controller 210 performswireless communication using a change of a magnetic field.

Further, although not shown, the mobile terminal 200 may selectivelyinclude units having an additional function, such as a camera module forphotographing an image or a moving picture, broadcasting receptionmodule for receiving digital broadcasting, audio signal output devicesuch as a speaker, sound signal input device such as a microphone, anddigital sound reproduction module such as an MP3 module. Such units canbe variously modified according to a convergence trend of digitaldevices and be additionally included in the mobile terminal 200according to the present exemplary embodiment.

The charging pad 100 and the mobile terminal 200 perform wirelesscommunication using a magnetic field, however the present invention isnot limited thereto. That is, a wireless charging system according tothe present exemplary embodiment may further include a separate wirelesscommunication module (for example, a Bluetooth® module, ZigBee module,Ultra Wide Band (UWB) module, or infrared ray communication module).

FIG. 5 illustrates a charging process in the charging pad 100 of FIG. 3.

In order to perform a charging operation, the mobile terminal 200 ispositioned on the charging pad 100.

Referring to FIG. 5, the first controller 110 determines a contact ofthe mobile terminal 200 on the charging pad 100 using the detection unit160 (block 501). Here, the detection unit 160 may be a pressuredetection sensor.

The first controller 110 determines a coordinate of the mobile terminal200 (block 503).

The first controller 110 moves the first coil 140 to a locationcorresponding to that of the mobile terminal 200 (block 505). Here, thefirst coil 140 is a kind of an electromagnet and generates a magneticfield when power is supplied. The first coil 140 may be, for example, asolenoid. It is preferable that the first coil 140 is formed small inconsideration of mobility and in order to minimize an influence of amagnetic field generated when power is supplied exerts on anotherelectronic device.

The first controller 110 determines whether the mobile terminal 200 is acertified device (block 507), For this, the charging pad 100 and themobile terminal 200 perform magnetic field communication using a changeof a magnetic field. Alternatively, the charging pad 100 and the mobileterminal 200 can perform communication using a separate wirelesscommunication module (for example, a Bluetooth® module, ZigBee module,infrared ray communication module, or UWB module). For this, thecharging pad 100 according to the present exemplary embodiment storesfirst certification information for determining whether the mobileterminal 200 is a chargeable device, and the mobile terminal 200 storessecond certification information representing that the mobile terminal200 is a chargeable device.

If the mobile terminal 200 is not a certified device, the firstcontroller 110 terminates a charging process according to the presentexemplary embodiment. If the mobile terminal 200 is a certified device,the first controller 110 supplies power to the first coil 140 and startswireless charging according to the present exemplary embodiment (block509). In this case, the mobile terminal 200 positioned on the chargingpad 100 charges a battery using an induced current generated by amagnetic field generating in the first coil 140.

The first controller 110 determines whether a control signal forrequesting location movement of the first coil 140 is received (block511). The mobile terminal 200 measures charging efficiency, and when thecharging efficiency is less than a preset reference value, the controlsignal is a signal transmitting to optimize charging efficiency.

If the control signal is received at block 511, the first controller 110moves the first coil 140 in a specific direction by a predetermineddistance (block 513). In this case, the mobile terminal 200 changes amoving direction of the first coil 140 according to increase or decreaseof charging efficiency. That is, after the first coil 140 is moved, ifcharging efficiency decreases, the mobile terminal 200 controls thefirst coil 140 to move in an opposite direction. Thereafter, the processreturns to block 511 and the first controller 110 determines whether acontrol signal for requesting location movement of the first coil 140 isreceived. That is, block 511 is repeated until the charging efficiencybecomes a preset reference value or more.

If charging efficiency is a preset reference value or more at block 511and if the control signal is not received, the first controller 110determines whether a charging completion message is received from themobile terminal 200 (block 515).

If a charging completion message is not received from the mobileterminal 200, block 515 continues to perform. If a charging completionmessage is received from the mobile terminal 200, the first controller110 terminates a charging process according to the present exemplaryembodiment. In this case, the first controller 110 interrupts powersupplied to the first coil 140. Thereafter, the first controller 110moves the first coil 140 to a location that does not correspond to themobile terminal 200. This is to prevent phenomenon in which electriccharging is not terminated as a result of power leaking to the firstcoil 140.

FIG. 6 illustrates a process of charging the mobile terminal 200 of FIG.4.

The mobile terminal 200 is positioned on the charging pad 100 and acertification process of the mobile terminal 200 is illustrated.

Referring to FIG. 6, the second controller 210 is in a standby state(block 600).

The second controller 210 determines whether a request for certificatingis received (block 601). The request for certificating is performed todetermine whether the mobile terminal 200 is a chargeable terminal.

If a request for certificating is not received, the second controller210 continues to perform block 601. If a request for certificating isreceived, the second controller 210 transmits certification informationto the charging pad 100 (block 603).

The second controller 210 determines an induced current or a voltagevalue generated in the second coil 260 and measures charging efficiency(block 605).

The second controller 210 determines whether the charging efficiency isless than a preset reference value (block 606).

If the charging efficiency is less than a preset reference value, thesecond controller 210 transmits a control signal for requesting locationmovement of the first coil 140 to the charging pad 100 (block 609).Thereafter, the process returns to block 605 and the second controller210 measures charging efficiency. Such a process is repeated until thecharging efficiency becomes a reference value or more.

If the charging efficiency is a preset reference value or more (block606), the second controller 210 determines whether electric charging iscomplete (block 607).

If electric charging is not complete, block 607 continues to perform. Ifelectric charging is complete, the second controller 210 transmits acharging completion message to the charging pad 100 (block 608). In thiscase, the charging pad 100, in response to receiving the chargingcompletion message, interrupts power supply to the first coil 140,thereby terminating electric charging.

As described above, in a method of wireless charging according to thepresent invention, even if the mobile terminal 200 is not positioned ata predetermined location in order to optimize charging efficiency,optimum charging efficiency can be sustained and because optimumcharging efficiency is substantially always sustained, a charging timeperiod can be minimized, and the wireless charging method can becommonly used for various mobile terminals.

Further, by minimizing a size of the first coil included in the chargingpad, an influence on performance and a lifetime of parts of the mobileterminal due to a magnetic field of the first coil can be minimized andstability of the mobile terminal can thus be secured.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A terminal comprising: a first coil configured tocharge a battery using an induction current induced to the first coil bya magnetic field generated by an external device adjacent to theterminal; a communication unit configured to transmit a control signalto the external device, the control signal being a command requestingthe external device to move a location of a second coil formed in theexternal device; and a control unit configured to check a chargingefficiency and to control the communication unit to transmit the controlsignal to the external device when the charging efficiency is less thana threshold.
 2. The terminal of claim 1, wherein: the communication unitis further configured to transmit a charging completion message to theexternal device, the charging completion message being a commandrequesting the external device to terminate charging process, and thecontrol unit is further configured to determine whether the charging ofthe battery is completed and to control the communication unit totransmit the charging completion message to the external device when thecharging of the battery is determined to be completed.
 3. The terminalof claim 2, wherein when the external device receives the chargingcompletion message, the external device interrupts a power supply forcharging the battery in the terminal to the second coil.
 4. The terminalof claim 2, wherein when the external device receives the chargingcompletion message, the external device moves the second coil to alocation that does not correspond to a location of the first coil. 5.The terminal of claim 1, wherein the communication unit is furtherconfigured to transmit certification information to the external device,the certification information being used by the external device todetermine whether the terminal is adequate for a wireless charging. 6.The terminal of claim 5, wherein when the external device fails toreceive correct certification information, the external device does notstart charging process.
 7. The terminal of claim 1, wherein thecommunication unit is configured to transmit the control signal throughshort range wireless communication.
 8. The terminal of claim 1, whereinwhen the external device receives the control signal, the externaldevice moves the location of the second coil.
 9. A method of a terminal,the terminal comprising a first coil configured to charge a batteryusing an induction current induced to the first coil by a magnetic fieldgenerated by an external device adjacent to the terminal, the methodcomprising: determining a charging efficiency; and transmitting acontrol signal to the external device when the charging efficiency isless than a threshold, the control signal being a command requesting theexternal device to move a location of a second coil formed in theexternal device.
 10. The method of claim 9, further comprising:determining whether the charging of the battery is completed; andtransmitting a charging completion message to the external device whenthe charging of the battery is determined to be completed, the chargingcompletion message being a command requesting the external device toterminate charging process.
 11. The method of claim 10, wherein when theexternal device receives the charging completion message, the externaldevice interrupts a power supply for charging the battery in theterminal to the second coil.
 12. The method of claim 10, wherein whenthe external device receives the charging completion message, theexternal device moves the second coil to a location that does notcorrespond to a location of the first coil.
 13. The method of claim 9,further comprising: transmitting certification information to theexternal device, the certification information being used by theexternal device for determining whether the terminal is adequate for awireless charging.
 14. The method of claim 13, wherein when the externaldevice fails to receive correct certification information, the externaldevice does not start charging process.
 15. The method of claim 9,wherein the control signal is transmitted through short range wirelesscommunication.
 16. The method of claim 9, wherein when the externaldevice receives the control signal, the external device moves thelocation of the second coil.
 17. A wireless charging system, comprising:a charging pad configured to generate a magnetic field when power issupplied; and a terminal adjacent to the charging pad, the terminalcomprising: a first coil configured to charge a battery using aninduction current induced to the first coil by a magnetic fieldgenerated by the charging pad; a communication unit configured totransmit a control signal to the external device, the control signalbeing a command requesting the external device to move a location of asecond coil formed in the charging pad; and a control unit configured todetermine a charging efficiency and to control the communication unit totransmit the control signal to the charging pad when the chargingefficiency is determined to be less than a threshold.
 18. The wirelesscharging system of claim 17, wherein: the communication unit is furtherconfigured to transmit a charging completion message to the chargingpad, the charging completion message being a command requesting thecharging pad to terminate charging process, and the control unit isfurther configured to determine whether the charging of the battery iscompleted and to control the communication unit to transmit the chargingcompletion message to the charging pad when the charging of the batteryis determined to be completed.
 19. The wireless charging system of claim17, wherein the communication unit is further configured to transmitcertification information to the charging pad, the certificationinformation being used by the charging pad to determine whether theterminal is adequate for a wireless charging.
 20. The wireless chargingsystem of claim 17, wherein the communication unit is configured totransmit the control signal through short range wireless communication.